TMC uses wetland plants to clean polluted lakes

Several small floating 'oasis' of green plants have been helping Thane Municipal Corporation (TMC) to clean its polluted lakes that too in an environment-friendly manner. The pilot project has been initiated in three lakes. The result is that water quality has improved and there is reduction in the foul odour from the lakes.

The pilot project is being carried out under the guidance of National Environmental Engineering Research Institute (NEERI) using Floating Wetlands or 'Florafts'. It involves planting certain varieties of plants in rafts that helps fight pollution.

According to officials from the TMC it was in 2004 that bio re-mediation was initiated with funding from the ministry of environment and forest and an aeration system was introduced to raise dissolved oxygen level. A special type of bacteria was introduced, but pollution and debris from surrounding slums did not allow the lakes to improve.

With the help of NEERI, the TMC initiated the pilot project in November, 2014, for three lakes-- Siddheshwar lake near the TMC office, Datiwali lake near Diva and Owla Lake at Ghodbunder Road. The surrounding slums that discharged sewage resulted in heavy growth of water hyacinth and weeds. This caused fishes to die and a foul odour.

Dr Rakesh Kumar, director, NEERI said that the TMC is using 'Florafts' technology that uses wetland plants like Canna, Scripus, Cyperus, Typha, Phragmites etc in 10ft X 10ft rafts, suspended in lakes.

Kumar added, "The roots of these plants take up pollutants from the water like excess nitrogen and phosphorus. They increase dissolved oxygen content and help trap sediments, thus serving as feeding and breeding grounds for dragonflies, birds and fishes as well." He added that all three lakes have different numbers of florafts. Siddheshwar lake has 25 florafts, Datiwali lake has 10 and each one weighs 150 kg taking care of 50 to 100 square metres of water area.

According to officials, earlier the dissolved oxygen in the three lakes was around 0.1 or 0.0 mg/l but now the level has increased to 2.5 to 3 mg/l. The ideal dissolve oxygen level for good flowing water is around 6 to 7 mg/l.

Manisha Pradhan, pollution control officer, for the TMC said that using this technology has given positive results. "We have seen that dissolved oxygen level has slightly improved and foul odour has reduced. We don't need aerators anymore, saving on maintenance costs and electricity bills," she said.

WHAT'S KILLING THE LAKES:

Experts say that with constant sewage containing high levels of phosphate, nitrates and others leads to growth of water weeds and water hyacinth that cover the lakes. These also use up high levels of oxygen thus reducing dissolved oxygen levels. Water bodies are covered , letting little sunlight penetrate the water. The immediate results of depleting oxygen levels in the lake is that fishes and other aquatic species start dying and water starts developing a foul smell.